googleapis/mcp-toolbox · error

failed to marshal job to JSON: %w

Error message

failed to marshal job to JSON: %w

What it means

After fetching the job proto, GetJob serializes it to JSON with protojson.Marshal. This error means protojson failed to marshal the *dataprocpb.Job. This is rare and usually indicates an invalid or corrupt proto message (e.g. a proto with invalid field state produced by custom middleware or an incompatible library version).

Source

Thrown at internal/sources/dataproc/dataproc.go:405

// GetJob gets a single job.
func (s *Source) GetJob(ctx context.Context, jobId string) (any, error) {
	client := s.GetJobControllerClient()

	req := &dataprocpb.GetJobRequest{
		ProjectId: s.Project,
		Region:    s.Region,
		JobId:     jobId,
	}

	jobPb, err := client.GetJob(ctx, req)
	if err != nil {
		return nil, fmt.Errorf("failed to get job: %w", err)
	}

	jsonBytes, err := protojson.Marshal(jobPb)
	if err != nil {
		return nil, fmt.Errorf("failed to marshal job to JSON: %w", err)
	}

	var result map[string]any
	if err := json.Unmarshal(jsonBytes, &result); err != nil {
		return nil, fmt.Errorf("failed to unmarshal job JSON: %w", err)
	}

	consoleUrl := JobConsoleURLFromProto(jobPb, s.Region)
	logsUrl, err := JobLogsURLFromProto(jobPb, s.Region)
	if err != nil {
		return nil, fmt.Errorf("error generating logs url: %v", err)
	}

	wrappedResult := map[string]any{
		"consoleUrl": consoleUrl,
		"logsUrl":    logsUrl,
		"job":        result,
	}

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Check go.mod for mismatched google.golang.org/protobuf versions and run go mod tidy
2. Regenerate vendored dataprocpb code if protos were customized
3. Log the error and retry GetJob; the failure is usually not deterministic in application logic

Example fix

// before
require google.golang.org/protobuf v1.30.0
// after
require google.golang.org/protobuf v1.33.0 // align with generated code, then: go mod tidy

job, err := svc.GetJob(ctx, jobId)
if err != nil && strings.Contains(err.Error(), "marshal job to JSON") {
	// retry once; if persistent, align protobuf library versions
}

When it happens

Trigger: protojson.Marshal returning an error on the fetched Job proto — practically only when the proto is in an invalid state (e.g. invalid oneof contents or incompatible google.golang.org/protobuf versions).

Common situations: Version skew between google.golang.org/protobuf and generated pb code; patched/instrumented protos; extremely rare in normal use.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• failed to unmarshal job JSON: %w
• operation finished with error but could not marshal error ob
• failed to marshal operation to JSON: %w
• failed to create dataproc client: %w
• failed to create longrunning client: %w

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/d0c64cc48b2e12e0. Report an issue: GitHub.